1. Field of the Invention
The present invention relates, in general, to micro-electro-mechanical system (MEMS) packages with metal sealing members and methods of manufacturing the MEMS packages and, more particularly, to an MEMS package having a metal sealing member, in which an MEMS element provided on a substrate is hermetically sealed from the external environment by forming a metal layer on the substrate by patterning, or forming a spacer on the substrate so as to create an MEMS moving space in which the MEMS element is free to move vertically; joining a lid to the metal layer or the spacer; providing a side sealing member on a side surface of the lid; and covering the lid and the substrate with the metal sealing member.
2. Description of the Related Art
In recent years, high-capacity communications for broadband service, such as in the Internet or the IMT 2000, have become powerful, so that optical communication techniques including, for example, WDM (wavelength division multiplexing), have been quickly standardized. In relation to the standardization of the optical communication technique, MEMS, which does not depend on wavelength, data rate or signal format and thereby has characteristics of being “optically transparent”, has been proposed and recognized as an innovative technique to supplant electronics, which can accomplish the recent trend of system smallness.
In the related art, current applications of MEMS are accelerometers, pressure sensors, inkjet heads, hard disk heads, projection displays, scanners and micro-fluidics. In recent years, interest in the techniques of optical communication elements, having higher operational performance to meet the rapid development in the optical communications field, has increased.
Particularly, the interest in the techniques of the optical communication elements is concentrated on spatial light modulators, which have a great number of micromirrors and operate in a specified switching manner such that the micromirrors are actuated by MEMS type actuators. The spatial light modulators use an optical signal processing technique with advantages in that a great amount of data can be quickly processed in a parallel manner, unlike a conventional digital information processing technique, in which a great amount of data cannot be processed in real time.
Thus, studies have been actively conducted on the design and production of binary phase only filters, optical logic gates, light amplifiers, image processing techniques, optical devices, and light modulators using the spatial light modulation theory. Of them, the spatial light modulators are applied to fields relating to optical memory units, optical display devices, printers, optical interconnections, and holograms, and studies have been conducted to develop display devices employing the spatial display modulators.
However, the MEMS elements have ultra-fine actuators so that the MEMS elements are greatly sensitive to the external environment, including temperature, humidity, micro-dust, vibration and impact, and thereby may frequently commit errors during operation, or may suddenly stop operating.
In an effort to allow the MEMS elements to effectively operate without being negatively affected by the environment, the MEMS elements have been sealed in cavities of sealed packages. U.S. Pat. No. 6,303,986 discloses a method and apparatus for sealing MEMS elements using a hermetic lid to provide an MEMS package.
Herein below, the construction of the MEMS package disclosed in U.S. Pat. No. 6,303,986, in which the lid glass hermetically seals the MEMS elements from the external environment, will be described with reference to FIG. 1.
FIG. 1 shows a representative sectional view of the MEMS package in which the transparent lid hermetically seals the MEMS element. As shown in FIG. 1, a conductive ribbon 100 having a metallic conductive/reflective covering 102 is formed over an upper surface of a semiconductor substrate 104, with an air gap 106 defined between the ribbon 100 and the substrate 104.
A conductive electrode 108 is formed on the upper surface of the substrate 104 and covered with an insulation layer 110. The conductive electrode 108 is placed under the ribbon 100 at a position under the air gap 106.
The conductive/reflective covering 102 extends beyond the region of the mechanically active ribbon 100 and is configured as a bond pad 112 at its distal end. The MEMS package is also passivated with a conventional overlying insulating passivation layer 114 which does not cover the bond pads 112 or the ribbon structures 100 and 102.
Control and power signals are coupled to the MEMS package using conventional wire-bonding structures 116.
Unlike conventional semiconductor manufacturing techniques in which semiconductor elements are packed densely onto the upper surface of a semiconductor substrate, an optical glass is hermetically sealed directly onto the semiconductor substrate in the above-mentioned US patent. Thus, the bond pads 112 are spaced a considerable distance from the ribbon structures 100 and 102, so that a lid sealing region 118 is provided. A solderable material 120 is formed on the lid sealing region 118.
The hermetic lid 122, which is joined to the semiconductor substrate, is preferably formed of an optical quality material. Thus, the lid 122 can be used for a variety of purposes including filtering undesired radiation and enhancing or decreasing reflectivity.
The lid 122 may be also coated with an optically sensitive material to be used for other purposes without being limited to the above-mentioned purposes.
Once the lid 122 is formed to a size appropriate to fit concurrently over the lid sealing region 118, with a solderable material 124 formed in a ring surrounding the periphery of one surface of the lid 122, solder 126 is deposited onto the solderable material 124 so that the lid 122 is joined to the semiconductor substrate.
Though not shown to scale in the drawing, a significant space exists between the lid 122 and the ribbon structures 100 and 102 to prevent them from interfering with one another. Thus, the ribbon structures 100 and 102 are free to move upwards and downwards.
However, in the above-mentioned conventional technique of sealing the semiconductor elements in the above-mentioned MEMS package, the solder must be placed between the substrate and the lid and, thereafter, heat must be applied to the solder through a reflow process at a predetermined temperature so as to bond the lid to the substrate. Thus, the technique undesirably reduces the work speed, causing a reduction in productivity.
Another problem of the technique of sealing the semiconductor elements in the MEMS package is that it is impossible to execute a reworking process, such as for adding solder, even when the sealing is not complete due to inaccurate positioning of the solder and/or application of a deficient amount of solder to the junction between the substrate and the lid.